The replacement of body fluids in the region of mucous membranes and internal cavities of the body which are coated with mucous membrane or epithelial cells (apart from blood vessels) is at present a typical application for aqueous liquids such as for example tear-replacement substances in the lachrymal ducts or artificial saliva in the region of the oral cavity, but also for silicone oil or fluorocarbon liquids which are used as endotamponades in the region of the vitreous body of the eye (as described for example in U.S. Pat. No. 5,258,412).
The special feature of the human or animal body surface is that aqueous liquids are subject to an extensive exchange of substances there as a rule and thus usually remain for an undesirably short time on the body surface. In contrast, oils, such as for example silicone oils, are provided as a rule as surface therapeutic agents which remain for a long time. Intraocular tamponades (endotamponades) based on silicone oil are even agents which remain permanently or which have to be removed after some time.
Oils, then, are generally used in medicine when a high interfacial tension and a low interaction with the aqueous systems of the body are desired. Oils are broken down only with the addition of emulsifiers or specific enzyme systems. A natural breaking down of silicone oil is not possible since the body has no suitable enzyme system for splitting the molecules. Low-molecular portions of the silicone oil are suspected, however, of being a cause of certain degenerative processes in the body. In this way, damage to the neuronal apparatus of the retina are attributed to them for example when used as a vitreous body replacement substance (Saitoh et al., Long-term effect on optic nerve of silicone oil tamponade in rabbits: histological and EDXA findings. Eye, 2002, 16(2):171-176; Agrawal et al., Silicone oil-associated optic nerve degeneration. Am. J. Ophthalmol., 2002 133(3):429-430).
Other bio-compatible substances with high surface tension and little tendency to foam formation (emulsification) are therefore in principle attractive candidates for the replacement of vitreous bodies, tears and for the non-aqueous treatment of skin and mucous membranes.
In the scope of his research work the Applicant has established that a specific substance which is already known per se and is like oil but not like silicone oil is excellently suitable as a body replacement substance and can be used for example as an artificial tear substance or as an artificial vitreous body without any drawbacks.
This substance already known per se and on the market is dimer diol. In the present application dimer diols are understood to be predominantly products containing aliphatic or cycloaliphatic bivalent alcohols which are generally obtained by the dimerization of unsaturated fatty acids and the subsequent reduction of the acid groups to form hydroxyl groups. Dimer diols of this type have been in widespread use for decades, for example in the form of monomers for the production of plastics, in particular of polyurethanes (see for example DE 43 08 100, WO 95/34592).
Dimer diols are likewise already known in cosmetic and pharmaceutical compositions, where they are used, however, only in small portions which do not exceed approximately 20% (see for example EP 1 471 898, DE 195 07 203, US 2001/0018424 and WO 98/47366).
To the best of the Applicant's knowledge, however, dimer diols in a relatively pure form have until now never been considered for medical use. The Applicant has tested dimer diols for their bio-compatibility and has found that these substances have an excellent compatibility on the surface of the eye as well as in contact with the nerve fibre layer of the inside of the eye. Dimer diol can therefore advantageously replace the silicone oils used until now.
Dimer diols are clearly transparent and do not mix with water. They are suitable for producing a lipid layer of high surface tension on the surface of the eye and in the interior of the eye as well as on any other mucous membrane and body cavity. In this way, these substances are excellently suitable for stabilizing and packing sensitive surfaces on account of the high surface tension, as is necessary in the case of an internal splinting of the retina by a vitreous body replacement substance.